Trigonal Unit Research Articles

On the CN-K coordination modes in Kn[M6-n(CN)6]·xH2O: first evidence of CN-K electron-deficient bonding.

Based on the determination of single crystal XRD structures of potassium hexacyanidometallates and on IR, and Raman data, here we propose for the first time the occurrence of an electron-deficient bonding between the N end of the CN- ligand and the K+ metal center. The crystal structures of Kn[M6-n(CN)6]·xH2O (M = Fe(ii), Ru(ii), Os(ii), Co(iii), Rh(iii), Ir(iii), Pt(iv)) reveal the presence of four types of CN-K interactions: (i) a linear CN-K bond, (ii) the N ends in a bipodal coordination involving two K atoms, (iii) the N ends in a tripodal coordination mode involving three K atoms and (iv) the N ends and the K atoms with the largest K-N distances within the subseries that can be attributed to the electrostatic interactions. The bi- and tripodal coordination modes between the N end of the CN- ligand and K+ ions are atypical and their nature is discussed in this contribution. The CN- ligand N end can behave as a two-electron donor that participates in a three-center two-electron bonding (i.e. Class II μ-L 3c-2e) for a N-bipodal coordination mode or as a two-electron donor that participates in a four-center two-electron bonding (4c-2e) for an N-tripodal coordination mode. Such a possibility is closely related to the π-back donation ability of the CN- ligand, which results in a charge density accumulation on the N end, which could be partially donated to the K atom through an σ-mechanism. For the divalent metals (Fe, Ru, Os), the solids crystallize with a monoclinic unit cell in the C2/c space group, while for the trivalent ones (Co, Rh, Ir), the crystal structure corresponds to an orthorhombic unit cell in the Pbcn space group. Potassium hexacyanidoplatinate(iv) crystallizes with a trigonal unit cell, in the P3[combining macron]1m space group, where each N end is always found coordinating two K atoms. The finding of these novel coordination modes of the CN- ligands, relying on an electron-deficient bonding behavior, paves the way for the design of functional materials based on hexacyanidometallates. The experimental results and the proposed electron-deficient bonding model herein discussed were appropriately supported by the computational calculations.

A Novel Approach to Transform Bitmap to Vector Image for Data Reliable Visualization considering the Image Triangulation and Color Selection

Vector image is a type of image composed of many geometric primitives. Compared with bitmaps, vector images have the ability to save memory as well as to enlarge without distortion. Meanwhile, it has been commonly adopted in data visualization (image data) because it can be scaled to multiple sizes to fit different scenes. For instance, it can be applied for the illustrations in newspapers and magazines, the logo on the web, the background for poster, the design of text, and traffic signs. However, transforming a bitmap to vector image is still a challenging problem because of the complicated content of a bitmap, which tends to consist of more than just simple geometry. Aiming at this issue, there is a new approach proposed to transform from bitmaps to vector images, which is based on triangle units and consists of three steps. In detail, firstly, there is an initial mesh constructed for one image in pixel level after detecting features. Then, the initial mesh will be simplified by collapsing two vertices as the initial mesh is too dense to represent one image. Specifically, there are two main parts in this step, which are collapse conditions and collapse influences. In the step of collapsing, issues such as overlap and sharp triangles can be conquered by a sort-edge method (which will be illustrated specifically later). The final step is to select one color for each triangle, since it is helpful to save the memory and speed up the process of this method. In addition, one color will represent one triangle; hence, in the final step, the four-triangle sample method will be applied in order to prevent a vector image from generating too large color discontinuity. Once the pretest proceeds without mistake, the method above is able to work for the general bitmaps. Note that our method can be applied to information security and privacy, since one image can be encoded to some triangles and colors.

Enhanced near-infrared luminescence at 1.07 μm of Nd3+ doped PbCl2–Li2B4O7 glasses for solid state laser and optical fiber amplifier applications

Abstract Nd3+ doped PbCl2–Li2B4O7 glasses have been synthesized using melt quenching technique. XRD spectra reveals the signature of non-crystalline behavior of synthesized glasses. DSC studies reveal glass transition temperature and thermal stability parameter (ΔT) exhibit composition dependent trends and ΔT is as high as 114 °C. UV–Vis spectra contain eleven well-defined absorption peaks with five intense absorption bands centered at 527, 586, 750, 806 and 876 nm which are assigned to transitions from 4I9/2 → 4G7/2, [4G5/2,2G7/2], [4F7/2, 4S3/2], [4F5/2, 2H9/2] and 4F3/2 respectively. The maximum absorption cross section 1 . 139 × 10 − 20 cm2 of 806 nm pump level transition 4I9/2 → [4F5/2, 2H9/2] is comparable with maximum absorption cross section 1 . 149 × 10 − 20 cm2 of 586 nm hypersensitive transition 4I9/2 → [4G5/2, 2G7/2]. Near infrared emission spectra exhibit very high emission intensity at 1070 nm for 4F3/2 → 4I11/2 transition along with two dominant emission bands at 904 and 1340 nm corresponding to 4F3/2 → 4I9/2 and 4F3/2 → 4I13/2 transitions. This high absorption and emission intensities are attributed to high degree of covalent environment of ligands surrounding Nd3+ ions. Bonding parameter, δ increase with Nd2O3 content which suggests dominance of covalency between Nd3+ ion and ligands. 11B MAS NMR studies reveal that, the addition of Nd2O3 to Li2B4O7 converts diborate units into chain-like network structures such as charged trigonal borate units which is further supported by FTIR study. Two photon absorption coefficient shows linear relationship with optical band gap energy. Hence Nd3+ doped PbCl2–Li2B4O7 glasses with superior absorption and emission properties are found to be potential candidates for near-infrared solid state laser and optical fiber amplifier applications.

Conformation and Aromaticity Switching in a Curved Non-Alternant sp2 Carbon Scaffold.

A curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd‐catalyzed [5+2] annulation from a 3,9‐diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly‐like motion. Stepwise oxidation produced radical cation 1 .+ and dication 1 2+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π‐overlap between the enantiomers. For the radical cation 1 .+, a less curved cisoid conformation is observed with a π‐dimer‐type arrangement. 1 2+ adopts a more planar structure with transoid conformation and slip‐stacked π‐overlap with closest neighbors. We also observed an intermolecular mixed‐valence complex of 1⋅(1 .+)3 that has a huge trigonal unit cell [(1)72(SbF6)54⋅(hexane)101] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

Conformation and Aromaticity Switching in a Curved Non‐Alternant sp2 Carbon Scaffold

AbstractA curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd‐catalyzed [5+2] annulation from a 3,9‐diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly‐like motion. Stepwise oxidation produced radical cation 1.+ and dication 12+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π‐overlap between the enantiomers. For the radical cation 1.+, a less curved cisoid conformation is observed with a π‐dimer‐type arrangement. 12+ adopts a more planar structure with transoid conformation and slip‐stacked π‐overlap with closest neighbors. We also observed an intermolecular mixed‐valence complex of 1⋅(1.+)3 that has a huge trigonal unit cell [(1)72(SbF6)54⋅(hexane)101] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

The influence of Ni2+ and other ions on the trigonal structure of DNA.

We present a new structure of a DNA dodecamer obtained in the presence of Ni2+ ions. The DNA forms Ni-guanine cross-links between neighboring molecules. Our results show that an adequate dosage of Ni2+ may help to form well-defined DNA nanostructures. We also compare our structure with other dodecamers which present unique features and also crystallize in trigonal unit cells, strongly influenced by the counterions associated with DNA. In all cases, the DNA duplexes form parallel pseudo-helical columns in the crystal, similar to DNA-protamine and native DNA fibers.

Optical and Structural Studies of B2O3–ZnO–Na2O–Li2O Glasses Containing Ag Nano Particles

B2O3–ZnO–Na2O–Li2O (BZNL) based glasses containing silver nano particles (Ag NPs) were prepared by melt-quenching technique. Four reducing agents such as Bi2O3, As2O3, Sb2O3, SnO were separately used to reduce Ag+ ions into Ago atoms in the form of nano particles. The glasses were characterized by XRD, FTIR, DSC, Optical absorption and Raman spectroscopy. The amorphous nature of the prepared glasses was confirmed through XRD and SEM measurements. The EDS spectra showed that all the added elements were present in the respective glasses. The vibrational features of various functional groups like stretching vibrations of B–O linkages in BO4 tetrahedral, asymmetric stretching vibrations of B–O bond in BO3 trigonal units and vibrations of Zn–O bonds from ZnO4 groups were identified by FTIR and Raman spectroscopy. From optical absorption studies it was observed that all prepared samples except SnO did not show characteristic surface plasmon resonance (SPR) band of Ag. Therefore, all the samples were heat treated at 500oC in accordance with DSC thermogram to form Ag nano particles. The formation of Ag nanoparticles was confirmed by optical absorption spectra. The doping of SnO to BZNL-Ag glass system could assist the growth of silver nano particles was showed by a sharp peak in optical absorption spectra at 410 nm as SPR band.

Remarkable Structural Diversity between Zr/Hf and Rare-Earth MOFs via Ligand Functionalization and the Discovery of Unique (4, 8)-c and (4, 12)-connected Frameworks.

Ligand modification in MOFs provides great opportunities not only for the development of functional materials with new or enhanced properties but also for the discovery of novel structures. We report here that a sulfone-functionalized tetrahedral carboxylate-based ligand is capable of directing the formation of new and fascinating MOFs when combined with Zr4+/Hf4+ and rare-earth metal cations (RE) with improved gas-sorption properties. In particular, the resulting M-flu-SO2 (M: Zr, Hf) materials display a new type of the augmented flu-a net, which is different as compared to the flu-a framework formed by the nonfunctionalized tetrahedral ligand. In terms of properties, a remarkable increase in the CO2 uptake is observed that reaches 76.6% and 61.6% at 273 and 298 K and 1 bar, respectively. When combined with REs, the sulfone-modified linker affords novel MOFs, RE-hpt-MOF-1 (RE: Y3+, Ho3+, Er3+), which displays a fascinating (4, 12)-coordinated hpt net, based on nonanuclear [RE9(μ3-Ο)2(μ3-ΟΗ)12(-COO)12] clusters that serve as hexagonal prismatic building blocks. In the absence of the sulfone groups, we discovered that the tetrahedral linker directs the formation of new RE-MOFs, RE-ken-MOF-1 (RE: Y3+, Ho3+, Er3+, Yb3+), that display an unprecedented (4, 8)-coordinated ken net based on nonanuclear RE9-clusters, to serve as bicapped trigonal prismatic building units. Successful activation of the representative member Y-ken-MOF-1 reveals a high BET surface area and total pore volume reaching 2621 m2 g-1 and 0.95 cm3 g-1, respectively. These values are the highest among all RE MOFs based on nonanuclear clusters and some of the highest in the entire RE family of MOFs. The present work uncovers a unique structural diversity existing between Zr/Hf and RE-based MOFs that demonstrates the crucial role of linker design. In addition, the discovery of the new RE-hpt-MOF-1 and RE-ken-MOF-1 families of MOFs highlights the great opportunities existing in RE-MOFs in terms of structural diversity that could lead to novel materials with new properties.

Flux Synthesis of a Metal Carbide Hydride Using Anthracene As a Reactant.

La15(FeC6)4H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La3.67FeC6, a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La15(FeC6)4H is metallic and is stabilized by the incorporation of hydride anions.

Rational Design of the Metal-Free KBe2 BO3 F2 ⋅(KBBF) Family Member C(NH2 )3 SO3 F with Ultraviolet Optical Nonlinearity.

The first fluorosulfonic ultraviolet (UV) nonlinear optical (NLO) material, C(NH2 )3 SO3 F, is rationally designed by taking KBe2 BO3 F2 (KBBF) as the parent compound. C(NH2 )3 SO3 F features similar topological layers as KBBF by replacing inorganic (BO3 )3- with organic C(NH2 )3 + trigonal units and BeO3 F with SO3 F- tetrahedra. Therefore, C(NH2 )3 SO3 F is a metal-free UV NLO crystal. Benefiting from the coplanar configuration of the C(NH2 )3 + cationic groups, it possesses a large SHG response of 5×KDP and moderate birefringence of 0.133@1064 nm. Besides, it has a short UV cutoff edge of 200 nm. The calculated results reveal the shortest SHG phase-matching wavelengths can reach 200 nm. These findings highlight the exploration of metal-free compounds as nontoxic and low-cost UV NLO materials as a new research area.

Rational Design of the Metal‐Free KBe2BO3F2⋅(KBBF) Family Member C(NH2)3SO3F with Ultraviolet Optical Nonlinearity

AbstractThe first fluorosulfonic ultraviolet (UV) nonlinear optical (NLO) material, C(NH2)3SO3F, is rationally designed by taking KBe2BO3F2 (KBBF) as the parent compound. C(NH2)3SO3F features similar topological layers as KBBF by replacing inorganic (BO3)3− with organic C(NH2)3+ trigonal units and BeO3F with SO3F− tetrahedra. Therefore, C(NH2)3SO3F is a metal‐free UV NLO crystal. Benefiting from the coplanar configuration of the C(NH2)3+ cationic groups, it possesses a large SHG response of 5×KDP and moderate birefringence of 0.133@1064 nm. Besides, it has a short UV cutoff edge of 200 nm. The calculated results reveal the shortest SHG phase‐matching wavelengths can reach 200 nm. These findings highlight the exploration of metal‐free compounds as nontoxic and low‐cost UV NLO materials as a new research area.

Optical Spectroscopy and Excited-State Dynamics of Eu3+ -Doped Bismuth Borate Glasses Containing CuO.

Bismuth borate glasses containing phosphors and luminescent rare-earths are of interest for applications in light-emitting devices. Herein, the influence of CuO impurities on red-emitting Eu3+ -doped bismuth borate glasses of the 25Bi2 O3 -15BaO-10Li2 O-50B2 O3 type was investigated by various spectroscopic methods. The glasses were prepared by the melt-quench technique and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV/Vis optical absorption (OA), and photoluminescence (PL) spectroscopy including decay kinetics assessment. The XRD data confirmed the amorphous nature of the glasses whereas FT-IR spectra indicated the basic structural features of trigonal BO3 units and BO4 tetrahedra. The OA analysis showed that addition of CuO up to 0.5 mol% results in significant growth of the visible Cu2+ absorption band around 715 nm, with slight decrease in the optical band gap energies assessed through Tauc plots. A drastic PL quenching of Eu3+ ions emission was evidenced concurring with the detrimental effect of Cu2+ . The assessment of the Eu3+ emission decay curves revealed significant lifetime decrease of the 5 D0 emitting state with increasing CuO concentration. An analysis of quenching constants was finally performed comparing results from integrated PL data with the emission decay rates. It is argued that the bismuth borate glass system supports an effective Eu3+ →Cu2+ energy transfer (more so than phosphates) in connection with a strong spectral overlap between Eu3+ emission and Cu2+ absorption.

Impact of substitution of B2O3 by Bi2O3 on the structural changes and associated oxygen defect centers in B2O3-TeO2 glass.

Bulk samples of compositions x(Bi2O3)-(0.5-x)(B2O3)-0.5(TeO2) with x = 0.05, 0.1, 0.2, 0.3 and 0.4 are prepared using melt quenching technique The IR absorbance revealed that at x = 0.05 the network is mainly constituted by [BiO3] and [BiO5], [BO3] trigonal pyramid and [BO4] tetrahedron, [TeO4] trigonal bipyramidal and [TeO3] trigonal pyramid structural units. Increasing Bi2O3 content over 0.05 transforms [BO4] to [BO3], [TeO3] to [TeO4] and [BiO3] into [BiO5]. The calculated ratio of BO4 in the structural network showed a decrease against the increase in Bi2O3which is explained according to the density of bridging and non-bridging oxygen defects. Temperature dependent capacitance-frequency measurements showed relaxation peaks which argued to the non-bridging Oxygen hole centers (NBOHC) trap defects. The emission rate of these NBOHC defects appeared that its energy states are located as deep levels with respect to the conduction band edge.

Six novel carbon and silicon allotropes with their potential application in photovoltaic field

By stacking up five novel cagelike structures, three novel three-dimensional (3D) sp3 bonding networks, named hP24, hP30 and hP36, were predicted in this work for the first time. These three newly discovered structures have trigonal unit cell with the space groups of P−3m1, P−3m1 and P3m1, respectively. Using first-principle calculations, the physical properties, including structural, mechanical, electronic and optical properties of C and Si in hP24, hP30 and hP36 phases were systematically studied. All these newly discovered carbon and silicon allotropes were proven to be thermodynamically and mechanically stable. The wide indirect bandgap value in range of 3.89–4.03 eV suggests that C in hP24, hP30 and hP36 phases have the potential to be applied in high frequency and high power electronic devices. The direct bandgap value in range of 0.60–1.16 eV, the smaller electron and hole effective mass than diamond-Si, and the significantly better photon absorption characteristics than diamond-Si suggest that hP24-Si, hP30-Si and hP36-Si are likely to have better performance in photovoltaic applications than diamond-Si. hP24-Si also has the potential to be applied in infrared detectors.

A comparative study on WO3 + MoO3 containing TeO2 and Sb2O3-based heavy metal oxide glasses

A series of tellurite and antimonite-based glasses were synthesized to compare different heavy metal oxide glass formers in terms of vitrification behavior and thermal, physical, optical and structural properties according to the changing MoO3 concentration. Substitution of glass formers for MoO3 resulted continuous structural transformation of TeO4 trigonal bipyramid and SbO3 units. The results revealed thatMoO3 has a dual function, i.e. former or modifier, in glass structure and in all studied glass compositions the ratio of network forming positions of MoO3 showed an increase with increasing MoO3 concentration. The direct allowed optical band gap energy values decreased with increasing temperature lying in the range 2.38 - 2.13 eV and found to be comparable with amorphous semiconductors for both glass forming systems. Antimonite glasses required higher melting temperatures and exhibited lower thermal stability and higher crystallization tendency. Therefore, tellurite glasses exhibited more suitable vitrification and thermal properties for opto-electronic applications.

Influence of doping transition metals and irradiation on some physical properties of borate glass

The optical absorption, FTIR and EPR spectra as well as the absorption dispersion parameters such as optical energy gap and urbach energy were studied. A series of 0.7% transition metal oxides (Ti, V, Cr, Fe) doped 70% B2O3–30% Bi2O3 glasses were prepared using conventional melting process. The valence states of TM ions and their coordination in the glass network have been investigated. FTIR spectra show that a gradual conversion of BO4 tetrahedral units into BO3 trigonal units in the glass network after irradiation (50 kGy) leading to the formation of non-bridging oxygen’s. The optical absorption and EPR studies suggest that, the TM-ions exist in the octahedral state and act as modifiers by increasing the degree of disorder in the glass network. Also, there is no remarkable change in the signal after irradiation which strongly recommended these glasses to be used as gamma radiation shielding.

Synthesis, structure and magnetic properties of a decanuclear Fe(III)/oxo cluster

An iron (III) cluster, namely [Fe10(μ3–O)8L8(NO3)6] (1), has been synthesized by treatment of Fe(NO3)3·9H2O with 3,5–dimethyl–1–(hydroxymethyl)–pyrazole (HL) under ambient temperature. The core skeleton of {FeIII10} can be regarded as a pear-like cage with eight triangular {FeIII3(μ3–O)} units, in which each three FeIII centers is held together by one μ3–O2− group with FeIII centers as corner-sharing triangle units. Importantly, {FeIII10} cluster is not only stable in solid state but also in solution, which is confirmed by powder X-ray diffraction (PXRD) pattern and electrospray ionization mass spectrometry (ESI-MS), respectively. Furthermore, 1 shows antiferromagnetic exchange behavior arising from the interactions between the iron(III) centers.

Thermal and optical properties of binary magnesium tellurite glasses and their link to the glass structure

Binary magnesium tellurite glasses x MgO, (100-x) TeO2, studied to determine their glass forming range, structure, thermal and optical properties. Glasses were successfully synthesis in the range x = 10–45 mol%. Addition of 50 mol% of MgO leads to the appearance of the Mg3TeO6 crystalline phase. The molar volume decreases linearly with increasing MgO content. Both glass transition and crystallization temperature increase with increasing MgO content. The deduced glass stabilities show a slight maximum for x = 25 and 30mol%. Studying the structure of these glasses using Raman spectroscopy reveals the transformation of trigonal bipyramid TeO4 (tbp) structural unit to the trigonal pyramid TeO3 units with the intermediate phase TeO3+1. The coordination of Te–O decreases with increasing MgO content. The UV–Vis spectra show a shift of the UV-cutoff toward higher energy and the measured refractive index decreases with increasing MgO. Optical band gap was estimated and the obtained values were used to calculate molar refractivity, molar polarizability and a calculated refractive index. The metallization criterion is found in the range (0.399–0.417) indicating good optical nonlinearity of the prepared glasses.

Correlation between acousto-optic and structural properties of Ge–Sb–S chalcogenide glasses

The acousto-optic properties of (100–x)GeS2-xSb2S3 (with x = 70, 60, 50, 40, 30, 20 mol%) and Ge12SbyS88-y (with y = 32, 25, 18 mol%) glasses were investigated, as well as the thermal and mechanical properties. The effects of Sb2S3 and Sb introduction on the structure and above-mentioned properties were discussed. For the first series of glasses: (100–x)GeS2-xSb2S3, the progressive introduction of Sb2S3 decreased the number of GeS4 units in the glass network. Consequently, the Vickers hardness, elastic modulus and stability of the glass against crystallization decreased dramatically. Increased acousto-optic figure of merit and increased acoustic attenuation were also observed. By contrast, for the second series of glasses Ge12SbyS88-y, some new long-chain structures were generated in addition to the increased SbS3 trigonal pyramid units in the glass networks with increased Sb content, which led to the opposite trend of the above performance except that the figure of merit increased. The maximum value with respect to the highest figure of merit was 252 × 10−18 s3/g obtained in Ge12Sb32S56 at 1550 nm and the corresponding acoustic attenuation was 1.95 dB/cm at 25 MHz ultrasonic frequency.

An unprecedented planar π-conjugated [B2P5]5- group with ultra-large birefringence and nonlinearity: an ab initio study.

Searching for new nonlinear optical active (NLO-active) units would greatly promote the development of NLO materials. Herein, we theoretically investigate a newly reported [B2P5]5- group which consisted of two corner-sharing [BP3]3- trigonal planar units. Attributed to the coplanar π-conjugated configuration and the unique connection mode, the [B2P5]5- group can achieve both the largest birefringence (Δn∼ 0.68) and nonlinearity (d15∼ 57.14 pm V-1) among all inorganic planar NLO-active groups, which makes it a good NLO-active unit. Our analysis also reveals that the modulation of the electronegativity of constituent elements upon replacing with the elements in the same period can effectively improve the NLO responses, which would inspire a new direction for designing high performing NLO materials.